Volatile vapor recovery system and method utilizing joule thompson expansion

ABSTRACT

A system for recovering volatile combustible liquids from a vapor stream includes a saturating vessel for rendering the vapor stream non-explosive, a plurality of high-pressure ambient aircooled condensing stages, each stage compressing the vapor stream and then cooling it to ambient temperature without the use of refrigeration for forming liquid product and residual vapors, an expansion vessel for receiving the vapors from the last condensing stage and further cooling and condensing them by Joule-Thompson expansion, means for returning recovered liquid product from the condensing stages and the expansion vessel to the saturating vessel, and means for venting the residual vapors from the expansion vessel. Means is also provided for cycling compressor coolant through one of the condensing stages.

United States Patent 11 1 1111 3,903,708 Mair Sept. 9, 1975 1 VOLATILE VAPOR RECOVERY SYSTEM 3.613.387 10/1971 Collins 62/514 x AND METHOD UTILIZING .IOULE THOMPSON EXPANSION Primary Evaminer-William F. ODea Assistant EraminerRonald C. Capossela [75] Inventor: James Mair Chicag- Attorney, Agenl. 0r Firm-Prangley, Dithmar, Vogel, [73] Assignee: General American Transportation Sandler & 'l

Corporation, Chicago, lll. [57] ABSTRACT [22] Flled' May 1973 A system for recovering volatile combustible liquids [2|] Appl. No.: 358,102 from a vapor stream includes a saturating vessel for rendering the vapor stream non-explosive, a plurality U 8 Cl 62/54 55/93 220/85 VR of high-pressure ambient air-cooled condensing stages. F13C /04 each stage compressing the vapor stream and the [58] g i 62 86 88 cooling it to ambient temperature without the use of refrigeration for forming liquid product and residual 62/514 220/85 :3 33 vapors, an expansion vessel for receiving the vapors from the last condensing stage and further cooling and condensing them by Joule-Thompson expansion, [56] References Cited means for returning recovered liquid product from the UNITED STATES PATENTS condensing stages and the expansion vessel to the satlR.l0 7/1933 Hamsbcrgcr 220/85 VR urating vessel, and means for venting the residual va- 2349J5U 3/1958 Tompkins, 230/35 VR pors from the expansion vessel. Means is also provided m z for cycling compressor coolant through one of the 21 en... 3,091,097 5/[963 Friant 62/40l x condensmg Stages 3,l88 824 6/1965 Geist ct 11],... 1, 62/5l4 9 Claims, 1 Drawing Figure VOLATILE VAPOR RECOVERY SYSTEM AND METHOD UTILIZING .IOULE THOMPSON EXPANSION The present invention relates to the recovery of volatile liquid product from a vapor stream, and more particularly to the recovery of combustible liquid product such as hydrocarbons. A typical application of the present invention would be in the recovery of vapors produced during the loading of gasoline and the like into the tank trucks at a loading terminal, in the interest of safety and the prevention of air pollution.

The present invention is an improvement of the invention disclosed in my copending application, Ser. No. l27,259, filed Mar. 23, l97l, entitled VOLATILE VAPOR RECOVERY SYSTEM and assigned to the assignee of the present invention, a general object of this present invention being to provide a vapor recovery system which discharges heat directly to the atmosphere without the use of refrigeration and returns the recovered liquid product to storage substantially at ambient temperature, thereby significantly reducing the power requirements of the system.

More particularly, it is an object of this invention to provide a method and apparatus for recovering volatile liquids from a vapor stream by compression and high pressure condensation of the vapors followed by Joule- Thompson expansion of the compressed vapors, all without the use of refrigeration.

It is an important object of the present invention to provide apparatus for recovering volatile liquids from a vapor stream, the apparatus comprising a plurality of stages of condensing apparatus, each of the stages including a compressor having an inlet and an outlet and ambient-air-cooled condensing means having an inlet connected to the outlet of the compressor and a vapor outlet and a liquid product outlet, the inlet of the first stage compressor being adapted for connection to an associated vapor source for receiving therefrom an input vapor stream, the inlet of the compressor of each of the other stages being connected to the vapor outlet of the condensing means of the immediately preceding stage for receiving the cooled vapor stream therefrom, vent means connected to the vapor outlet of the last stage condensing means for discharging to atmosphere the uncondensed vapor stream therefrom, and a liquid product reservoir connected to the liquid product outlets of the condensing means of each of the stages for receiving therefrom the recovered liquid product.

Still another object of the present invention is to provide apparatus of the type set forth, which includes an expansion vessel connected between the vent means and the vapor outlet of the last stage condensing means for further cooling and condensing the compressed vapor stream by JouleThompson expansion thereof, and means for returning the recovered liquid product from the expansion vessel to the liquid reservoir.

Still another object of the present invention is to provide a method for recovering volatile liquids from an input vapor stream, the method comprising the steps of compressing the input vapor stream in a plurality of compression stages. condensing the compressed vapor stream by cooling it with ambient air in a plurality of condensing stages alternating with the compression stages. venting to atmosphere the uncondensed vapor stream from the last condensing stage, and collecting the liquid product recovered in each of the condensing stages.

In connection with the foregoing object, still another object of this invention is to provide a method of the type set forth, which includes the step of further cooling and condensing the compressed vapor stream from the last condensing stage by Joule-Thompson expansion and collecting recovered liquid product of this expansion.

Further features of the invention pertain to the particular arrangement of the parts of the vapor recovery apparatus and the steps of the vapor recovery method whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advan tages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing, which is a diagrammatic representation of the vapor recovery system of the present invention, indicating the vapor and liquid flow paths therethrough.

With reference to the drawing, there is illustrated a vapor recovery system, generally designated by the numeral l0, constructed in accordance with and embodying the features of the present invention. The system 10 includes a vapor input conduit 11 adapted to be connected to an associated source of vapor (not shown). In a typical application of the present invention, the source of vapor may be a loading station for loading gasoline into the tank trucks or other vessels by the top loading method, the air-vapor mixture displaced from the truck tanks by the loading operation being collected by suitable vapor hoods or the like and fed into the vapor input conduit 11.

The conduit 11 is connected to a concentration correction vessel containing therein a body 21 of liquid product and a vapor space 22 thereabove. Preferably, the vapor input conduit 11 is connected to a manifold pipe I5 disposed along the bottom of the vessel 20 and immersed in the body 21 of liquid product for bubbling the input vapor stream up through the liquid product, thereby saturating the input vapors and insuring that the concentration of hydrocarbons therein shall be above the explosive limit. The concentration correc tion vessel 20 is connected to an entrainment separator by a vapor conduit 23 and a liquid product conduit 24, the entrainment separator 25 in turn being connected by a conduit 26 to a surge tank and by a conduit 27 to the first stage 36 of a two-stage compressor 35. The surge tank 30 is provided with a movable diaphragm 31 therein for forming a variable volume chamber in the surge tank 30. The diaphragm 31 is connected to a control switch 32, the switch 32 being responsive to movement of the diaphragm 31 for controlling the operation of the compressor 35 in a manner to be described more fully below.

The output of the first compressor stage 36 is connected by conduit 38 to the inlet of an ambient-aircooled condenser 40, which preferably includes cooling coils through which the vapor stream is passed and over which a stream of ambient air is forced by a suitable fan or blower. The outlet of the condenser 40 is connected by a conduit 41 to an inlet of a separator 42 which separates the condensed liquid from the uncon densed vapor stream. The separator 42 has a liquid product outlet which is connected by a conduit 43 to an inlet of the concentration correction vessel 20, the conduit 43 being provided with an automatic trap 44 therein for accommodating passage of liquid product from the separator 42 to the vessel 20 while maintaining the pressure differential therebetween. The separator 42 is also provided with a vapor outlet connected by a conduit 46 to the inlet of the second stage 37 of the compressor 35, the outlet of the compressor stage 37 being connected by a conduit 47 to the inlet of a second ambient-air-cooled condenser 50 which is substantially the same in construction and operation as the condenser 40. The outlet of the condenser 50 is connected by a conduit 51 to an inlet of a second separator 52, identical in construction and function to the separator 42. The separator 52 has a liquid product outlet connected by conduit 53 to another inlet of the separator 42, the conduit 53 being provided with an automatic trap 54 therein for accommodating passage of liquid product from the separator 52 to the separator 42 while maintaining the pressure differential therebe tween.

The separator 52 is also provided with a vapor outlet connected by a conduit 56 to the inlet of a Joule- Thompson expansion vessel 60, the conduit 56 being provided with a back pressure valve 55 for maintaining the system pressure established by the second compressor stage 37. The expansion vessel 60 has a liquid product outlet connected by a conduit 61 to another inlet of the concentration correction vessel 20, the conduit 61 preferably being provided with an automatic trap 62 for accommodating passage of liquid product from the expansion vessel 60 to the concentration correction vessel 20 while maintaining the pressure differential therebetween. The expansion vessel 60 has a vapor outlet connected by conduit 65 to the atmosphere for venting the uncondensed vapors, the conduit 65 preferably being provided with a back pressure valve 66 therein set at a relatively low pressure of approximately p.s.i.g. for maintaining a slight pressure differential between the expansion vessel 60 and the concentration vessel 20, thereby preventing backflow of liquid product from the vessel to the vessel 60.

The compressor 35 is preferably provided with a coolant such as glycol and water, and it is a feature of the present invention to utilize the condenser 50 for effecting cooling of this compressor coolant. More particularly, the coolant is fed from the second compressor stage 37 by a conduit 71 to a pump 70 which pumps the coolant through a conduit 72 to a separate section of the condenser 50 in which heat is rejected to atmosphere, the cooled liquid then being returned by a conduit 75 to the first stage 36 of the compressor 35. The conduit 72 is provided with a temperature controlled valve 75 therein adjusted to maintain optimum operating temperature in the compressor 35. Preferably, the pump 70 is connected so as to operate only when the compressor 35 is running.

The concentration correction vessel 20 is provided with a liquid product outlet connected by a conduit 8] and a pump 82 to a storage tank 86 for removing recovered liquid product from the vessel 20 and returning it to the storage tank 86. The vessel 20 is provided with a level control device 80 which is connected to a control valve 85 in the conduit 8]. the control device 80 being responsive to the level of liquid product in the vessel 20 for opening the valve 85 when the liquid product level exceeds a first predetermined level and for closing the valve when the liquid product level falls below a second predetermined level.

The operation of the vapor recovery system 10 will now be described in detail. For purposes of illustration, it is assumed that the input vapor stream flowing to the conduit 11 is a mixture of air and hydrocarbons at about 14.7 p.s.i.a. at F., it also being assumed that the ambient air temperature is approximately 90 F. The input vapor stream is fed via the conduit 11 in the manifold 15 to the interior of the concentration correction vessel 20, wherein it is bubbled up through the body of liquid product 21 for saturating the hydrocarbon vapors and insuring that the concentration thereof shall be above the explosive limit for gasoline vapors.

The air-vapor mixture then leaves the correction vessel 20 by way of the vapor conduit 23 and passes through the entrainment separator 25, entering tangentially to remove any entrained liquid from the vapor stream, liquid product removed in the entrainment separator being returned to the correction vessel 20 by the conduit 24. The vapor stream may then leave the sepa rator 25 by either or both of the conduits 26 and 27, the vapor passing through the conduit 26 entering the variable volume surge tank 30. Preferably, the compressor 35 is controlled by the switch 32 which is responsive to the volume of gas in the surge tank 30. More particu larly, as the volume and pressure of the gas stored in the surge tank 30 decreases below a predetermined minimum level, the diaphragm 31 moves downwardly for actuating the control switch 32 and de-energizing the compressor 35. Normally, when the compressor 35 is in operation, it draws the vapor stream through the conduit 27 from either or both of the correction vessel 20 or the surge tank 30. The input vapor stream will flow directly through the separator 25 to the compressor 35, with any excess vapor flow being temporarily stored in the surge tank 30. Then. when the input vapor stream through the conduit 11 reduces below the level required to properly feed the compressor 35, the vapors stored in the surge tank 30 are drawn off to the compressor 35, thereby permitting longer uninterrupted compressor operation and minimizing stoppage of the compressor.

The input vapor stream enters the first compressor stage 36 at approximately atmospheric pressure, the pressure of the vapor stream being raised by the compressor to about 65 p.s.i.a. and its temperature being raised to about 232 F. This hot compressed vapor mixture is passed through the conduit 38 to the inlet of the condenser 40, where it passes through cooling coils over which a stream of ambient air is blown by the blower. In the condenser 40, the temperature of the compressed vapor stream is reduced to near ambient temperature, i.e., to about 90-95 F., and, as the heat of compression is removed, the heavier hydrocarbons will condense until they reach their saturation point at the 65 p.s.i.a. pressure.

Then the mixture of cooled vapor and condensed liquid will pass through the conduit 41 to the separator 42. The condensed liquid will be discharged from the separator 42 by the automatic trap 44 through the conduit 43 and back to the concentration correction vessel 20, while the uncondensed vapor stream passes from the separator 42 through the conduit 46 to the suction of the second compressor stage 37. The input vapor stream which is at 65 p.s.i.a. and approximately 9()95 F. is compressed in the second compressor stage 37 to approximately 275 p.s.i.a., which raises its temperature to about 230 F. This further compressed vapor stream is then passed through the conduit 47 to the inlet of the second ambient-air-cooled condenser 50 in which the temperature of the vapor stream is again reduced by ambient-air-cooling to approximately ambient temperature, or 90-95 F. As the heat of compression is discharged to the atmosphere in the condenser 50, more hydrocarbons, including the balance of the heavier hydrocarbons and most of the lighter ones are condensed, and the liquid and vapor mixture passes from the condenser 50 through the conduit 51 to the inlet of the separator 52. The condensed liquid hydrocarbons are discharged from the separator 52 through the trap 54 and the conduit 53 to the separator 42. This liquid product, its pressure being reduced to 65 p.s.i.a. after it passes the trap 54, joins the liquid product in the separator 42 and passes therewith through the conduit 43 to the concentration correction vessel 20.

The uncondensed vapor stream leaves the separator 52 through the conduit 56 and the back pressure valve 55 to the expansion vessel 60, the back pressure valve 55 being set so as to maintain the system pressure of 275 p.s.i.a. established by the second compressor stage 37. As the vapor stream enters the expansion vessel 60, it is at 275 p.s.i.a. and approximately ambient tempera ture, the heat of compression having been removed by the condenser 50. In the vessel 60, the vapor stream undergoes Joule-Thompson expansion, whereby the vapor stream is further cooled by the Joule-Thompson effect and more of the lighter hydrocarbons are condensed. The condensed liquid product is discharged from the vessel 60 through the automatic trap 62 and the conduit 61 to the concentration correction vessel 20. The uncondensed residual vapors are vented to atmosphere from the vessel 60 through the conduit 65 and the back pressure valve 66, the valve 66 preferably being set at a relatively low pressure of approximately 5 p.s.i.g. so as to provide maximum expansion of the gas in the vessel 60, while maintaining a slight pressure differential between the vessel 60 and the concentration correction vessel 20.

As the recovered liquid product from the separators 24, 42, and 52 and the expansion vessel 60 accumulates in the concentration correction vessel 20 and exceeds the first predetermined level, the liquid level controller 80 opens the control valve 85 and permits the liquid product to be pumped through the conduit 81 by the pump 82 to the storage tank 86 until the level of liquid product in the vessel 20 has been reduced below a second predetermined level.

When the compressor 35 is running, the pump 70 pumps the compressor coolant from the cylinderjacket of the second compressor stage 37 through the conduits 7] and 72 to the separate section of the condenser 60 for discharging the heat to atmosphere, the cooled coolant then being returned through the conduit 76 to the cylinder jacket of the first compressor stage 36. Preferably. the pump 70 is connected to the compressor 35 and to the heat control valve 75 so that the pump is operable only when the compressor 35 is running and the control valve 75 is open. Thus, a predetermined optimum operating temperature may be contained in the compressor 35.

In a typical application of the vapor recovery system 10, the input vapor stream to the input conduit ll may be as follows:

Wt. Partial Wt. Fraction Press. Flow LB/ HR C .006 .09 6.4 C, .303 3.40 298.3 C,, .235 2,12 23|.5 C. .080 .6l 79.6 AIR .376 8.48 371.5

Total l-lC to compressor 615.8 LB/HR When the flow volume and composition of the input vapor stream is as indicated above, the vapor stream preferably enters the first compressor stage 36 at approximately l38 cubic feet per minute, the total hydrocarbon being fed to the compressor being equal to ap proximately 6l5.8 lb. per hour. With the system pressures as indicated above and with the ambient temperature assumed to be approximately 90 F., the vapor recovery system 10 is effective for recovering in excess of 90% of the hydrocarbons in the input vapor stream. More particularly, it is estimated that the total recovery of condensed hydrocarbons from the two condensers 40 and 50 will be as follows:

In addition, some additional hydrocarbons will be condensed in the expansion vessel 60, thereby insuring that well in excess of 90% of the hydrocarbons will be recovered by the vapor recovery system 10.

It is a significant feature of the present invention that this efficient recovery of the hydrocarbons from the input vapor stream is accomplished without the use of an external refrigeration system, thereby significantly decreasing the total power required to operate the system. ln addition, it will be appreciated that the vapor recovery system 10 of the present invention does away with the considerable cost of operation and maintenance of an external refrigeration system.

From the foregoing, it will be seen that there has been provided a novel and improved volatile vapor recovery system including a method and apparatus particularly adaptable for recovering combustible hydrocarbon vapors without the use of an external refrigeration system.

In addition, there has been provided a vapor recovery system which effects multi-stage compression and condensation of the vapor stream, with the condensation being effected through cooling of the compressed vapor stream by ambient air.

In addition, there has been provided a vapor recovery system of the character described, which further includes Joule-Thompson expansion of the cooled compressed vapor stream for effecting further cooling and condensation thereof.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in tht ppcnded claims all such modifications as. fa! within the true spirit and scope of the invention.

What is claimed is:

1. Apparatus for recovering volatile liquids from a vapor stream, said apparatus comprising a plurality of stages of condensing apparatus. each of said stages including a compressor having an inlet and an outlet and ambient-air-cooled condensing means having an inlet connected to the outlet of said compressor and a vapor outlet and a liquid product outlet, the inlet of the first stage compressor being adapted for connection to an associated vapor source for receiving therefrom an input vapor stream, the inlet of said compressor of each of the other stages being connected to the vapor outlet of said condensing means of the immediately preceding stage for receiving the cooled vapor stream therefrom, vent means connected to the vapor outlet of the last stage condensing means for discharging to atmosphere the uncondensed vapor stream therefrom, compressor cooling means for circulating a coolant other than said liquid product through said compressor in each of said stages and through said condensing means in one of said stages, and a liquid product reservoir connected to the liquid product outlets of said condensing means of each of said stages for receiving therefrom the recovered liquid product.

2. The apparatus set forth in claim 1, wherein the input vapor stream includes combustible hydrocarbons, said condensing apparatus included two stages, said first stage compressor compressing the vapor stream to approximately 65 p.s.i.a. at approximately 232 F., said second stage compressor further compressing the vapor stream to approximately 275 p.s.i.a. at approximately 230 F.

3. Apparatus for recovering volatile liquids from a vapor stream, said apparatus comprising a compressor having an inlet and an outlet, said inlet being adapted for connection to an associated vapor source for receiving therefrom an input vapor stream, ambient-aircooled condensing means having an inlet connected to the outlet of said compressor and a vapor outlet and a liquid product outlet, an expansion vessel having an inlet connected to the vapor outlet of said condensing means and a vapor outlet and a liquid product outlet, said expansion vessel effecting further cooling and condensing of the cooled compressed vapor stream from said condensing means by Joule-Thompson expansion thereof, vent means connected to the vapor outlet of said expansion vessel for discharging to the atmosphere the uncondensed vapor stream therefrom, and a liquid product reservior connected to the liquid product outlets of said condensing means and said expansion vessel for receiving therefrom the recovered liquid product.

4. The apparatus set forth in claim 3, wherein said expansion vessel reduces the pressure of the compressed vapor stream to approximately 5 p.s.i.g.

5. Apparatus for recovering volatile liquids from a vapor stream, said apparatus comprising a plurality of stages of condensing apparatus, each of said stages including a compressor having an inlet and an outlet and condensing means having an inlet connected to the outlet of said compressor and a vapor outlet and a liquid product outlet, the inlet of the first stage compressor being adapted for connection to an associated vapor source for receiving therefrom an input vapor stream, the inlet of said compressor of each of the other stages being connected to the vapor outlet of said condensing means of the immediately preceding stage for receiving the cooled vapor stream therefrom, an expansion vessel having an inlet connected to the vapor outlet of the last stage condensing means and a vapor outlet and a liquid product outlet, said expansion vessel effecting further cooling and condensing of the cooled compressed vapor stream from the last stage condensing means by Joule-Thompson expansion thereof, vent means connected to the vapor outlet of said expansion vessel for discharging to atmosphere the uncondensed vapor stream therefrom, and a liquid product reservoir connected to the liquid product outlets of said condensing means of each of said stages and said expansion vessel for receiving therefrom the recovered liquid product.

6. The apparatus set forth in claim 5, wherein the last stage compressor effects compression of the vapor stream to approximately 275 p.s.i.a. at approximately 230 F., said expansion vessel effecting expansion of the compressed vapor stream to approximately 5 p.s.i.g.

7. A method for recovering volatile liquids from an input vapor stream, said method comprising steps of compressing the input vapor stream in a plurality of compression stages, condensing the compressed vapor stream by cooling it in a plurality of condensing stages alternating with said compression stages, expanding the vapor stream from the last condensing stage by Joule- Thompson expansion for further cooling and condensing thereof, venting to atmosphere the uncondensed expanded vapors, and collecting the liquid product re covered in each of the condensing stages and the expansion step.

8. The method of claim 7, wherein the Joule Thompson expansion of the cooled compressed vapor stream effects reduction of the pressure thereof to approximately 5 p.s.i.g.

9. The method set forth in claim 7, wherein the input vapor stream includes a mixture of combustible hydrocarbons, and further including the step of correcting the concentration of the hydrocarbons of the input vapor stream to a non-explosive level. 

1. Apparatus for recovering volatile liquids from a vapor stream, said apparatus comprising a plurality of stages of condensing apparatus, each of said stages including a compressor having an inlet and an outlet and ambient-air-cooled condensing means having an inlet connected to the outlet of said compressor and a vapor outlet and a liquid product outlet, the inlet of the first stage compressor being adapted for connection to an associated vapor source for receiving therefrom an input vapor stream, the inlet of said compressor of each of the other stages being connected to the vapor outlet of said condensing means of the immediately preceding stage for receiving the cooled vapor stream therefrom, vent means connected to the vapor outlet of the last stage condensing means for discharging to atmosphere the uncondensed vapor stream therefrom, compressor cooling means for circulating a coolant other than said liquid product through said compressor in each of said stages and through said condensing means in one of said stages, and a liquid product reservoir connected to the liquid product outlets of said condensing means of each of said stages for receiving therefrom the recovered liquid product.
 2. The apparatus set forth in claim 1, wherein the input vapor stream includes combustible hydrocarbons, said condensing apparatus included two stages, said first stage compressor compressing the vapor stream to approximately 65 p.s.i.a. at approximately 232* F., said second stage compressor further compressing the vapor stream to approximately 275 p.s.i.a. at approximately 230* F.
 3. Apparatus for recovering volatile liquids from a vapor stream, said apparatus comprising a compressor having an inlet and an outlet, said inlet being adapted for connection to an associated vapor source for receiving therefrom an input vapor stream, aMbient-air-cooled condensing means having an inlet connected to the outlet of said compressor and a vapor outlet and a liquid product outlet, an expansion vessel having an inlet connected to the vapor outlet of said condensing means and a vapor outlet and a liquid product outlet, said expansion vessel effecting further cooling and condensing of the cooled compressed vapor stream from said condensing means by Joule-Thompson expansion thereof, vent means connected to the vapor outlet of said expansion vessel for discharging to the atmosphere the uncondensed vapor stream therefrom, and a liquid product reservior connected to the liquid product outlets of said condensing means and said expansion vessel for receiving therefrom the recovered liquid product.
 4. The apparatus set forth in claim 3, wherein said expansion vessel reduces the pressure of the compressed vapor stream to approximately 5 p.s.i.g.
 5. Apparatus for recovering volatile liquids from a vapor stream, said apparatus comprising a plurality of stages of condensing apparatus, each of said stages including a compressor having an inlet and an outlet and condensing means having an inlet connected to the outlet of said compressor and a vapor outlet and a liquid product outlet, the inlet of the first stage compressor being adapted for connection to an associated vapor source for receiving therefrom an input vapor stream, the inlet of said compressor of each of the other stages being connected to the vapor outlet of said condensing means of the immediately preceding stage for receiving the cooled vapor stream therefrom, an expansion vessel having an inlet connected to the vapor outlet of the last stage condensing means and a vapor outlet and a liquid product outlet, said expansion vessel effecting further cooling and condensing of the cooled compressed vapor stream from the last stage condensing means by Joule-Thompson expansion thereof, vent means connected to the vapor outlet of said expansion vessel for discharging to atmosphere the uncondensed vapor stream therefrom, and a liquid product reservoir connected to the liquid product outlets of said condensing means of each of said stages and said expansion vessel for receiving therefrom the recovered liquid product.
 6. The apparatus set forth in claim 5, wherein the last stage compressor effects compression of the vapor stream to approximately 275 p.s.i.a. at approximately 230* F., said expansion vessel effecting expansion of the compressed vapor stream to approximately 5 p.s.i.g.
 7. A method for recovering volatile liquids from an input vapor stream, said method comprising steps of compressing the input vapor stream in a plurality of compression stages, condensing the compressed vapor stream by cooling it in a plurality of condensing stages alternating with said compression stages, expanding the vapor stream from the last condensing stage by Joule-Thompson expansion for further cooling and condensing thereof, venting to atmosphere the uncondensed expanded vapors, and collecting the liquid product recovered in each of the condensing stages and the expansion step.
 8. The method of claim 7, wherein the Joule-Thompson expansion of the cooled compressed vapor stream effects reduction of the pressure thereof to approximately 5 p.s.i.g.
 9. The method set forth in claim 7, wherein the input vapor stream includes a mixture of combustible hydrocarbons, and further including the step of correcting the concentration of the hydrocarbons of the input vapor stream to a non-explosive level. 